.alpha.-L-aspartyl-L-phenylalanine methyl ester is a sweetening agent which is about 200 times sweeter than sucrose. The compound and its uses are extensively taught in U.S. Pat. Nos. 3,492,131; 3,642,491; and 3,780,189. A variety of methods for the economical synthesis of .alpha.-L-aspartyl-L-phenylalanine are known, for example, U.S. Pat. Nos. 3,933,781 and 4,173,562 describe the use of N-protected-L-aspartic anhydride in preparing .alpha.-L-aspartyl-L-phenylalanine methyl ester.
Chem Abstracts 64 19754C (1966) describes acetoacetyl derivatives of glycine, alanine, leucine, threonine, methionine and tryptophan made from the reaction of the corresponding amino acid with diketene. The acetoacetyl derivative of leucylglycine methyl ester is described in Tetrahedron Letters 10, 605-608 (1965). J. Chem Soc (C), 350, (1969) describes the preparation of N-acetoacetylvaline and N-acetoacetylvalyvaline from valine and valylvaline respectively and diketene.